1. Field of the Invention
The present invention relates to the non-metal catalyzed radical and living radical polymerization of halogen containing monomers such as vinyl halides and vinylidene halides. In particular, this invention relates to a process for the synthesis, in the presence of a non-metallic catalyst, of poly(vinyl chloride) (PVC) with controlled molecular weight and narrow molecular weight distribution. The polymerization can be initiated from various electron accepting radical precursors such as polyhalocarbons in the presence of non-metal reducing single electron transfer reagents as catalysts which can include low valent sulfur salts containing SO2 group. The process can be accelerated by electron shuttles such as alkyl viologens.
2. Description of the Prior Art
Heretofore, it was known to polymerize vinyl chloride (VC) and other vinyl halide monomers using conventional free radical processes. However, even in the presence of certain molecular weight additives, there is limited control over the molecular weight and polydispersity of the resulting polymer. In addition, VC polymers are thermally unstable and require thermal stabilizers for their practical use. Heretofore, there have been no methods reported to prepare poly(vinyl chloride) by a non-metal-catalyzed living process initiated from an active halide compound in which the molecular weight and the molecular weight distribution of PVC could be controlled.
Conventional free radical polymerization of vinyl chloride (VC) is accompanied by the formation of thermally labile tertiary and allylic chlorine defects which are responsible for the low thermal stability of poly(vinyl chloride). This provides its most relevant technological limitations. These structural defects are generated during the conventional radical polymerization of VC and are responsible for the initiation of a zipper mechanism of thermal degradation of PVC.
In U.S. patent Ser. No. 09/893,201, which is herein fully incorporated by reference, there is described a process for the living radical polymerization of vinyl halides utilizing a metal (preferably Cu) catalyst. The polymerization processes taught therein include both non-aqueous high temperature and aqueous room temperatures processes. The former gives polymers with low yields (maximum 30%) and high molecular weight distribution up to about 1.7. The latter achieves high conversions and lower molecular weight distribution (up to 1.50). Both processes show linear molecular weight dependence on the monomer conversion. A single electron transfer mechanism mediated by metals is proposed for the initiation and dormant species activation steps.
The PVC obtained by aqueous room temperature copper-catalyzed living radical polymerization of vinyl chloride as described in U.S. patent Ser. No. 09/893,201, contains a vanishingly small amount of carbon-carbon double bonds in comparison with conventional PVC. This allows us to consider such a polymer as one free of at least allylic chlorine defects that could lead to new properties. Alternatively, the use of heavy metal in polymerization processes requires an additional utilization of the spent catalyst and purification of the polymer, thereby increasing the cost.
Previously, attempts on living radical polymerization of vinyl halides, which did not involve metal catalysis, were based on degenerative chain transfer processes using iodine containing chain transfer agents and peroxy-esters as initiators. As is taught in U.S. Pat. No. 5,455,319, such a process was carried out at temperatures conventionally used for vinyl halide polymerizations. In addition, the polydispersity never decreased to values below 1.7.